I encountered something new this week; well, new to me, as I have never seen an RT Rejection rate of 26%. So I knew that was crazy high, as the normal rate is around 2-3%. So I had to go back to my ASME B31 Course and research an acceptable rate:
For most heavy industrial projects (oil and gas, power generation, chemical), the following percentages are typical:
1) World-Class/Elite: < 2%
This is the gold standard for high-pressure systems and nuclear applications.
2) Industry Average: 3% – 5%
Most mid-to-large scale pipeline and refinery projects operate within this window.
3) Warning Zone: > 5%
Rates exceeding 5% usually trigger "Three-Strike" rules for individual welders or mandatory retraining.
4) Critical Failure: > 10%
At this level, the cost of repairs and project delays often leads to a complete shutdown for a Root Cause Analysis (RCA).
It is important to note that codes like ASME B31.3 (Process Piping) or API 1104 (Pipelines) do not technically define an “acceptable” percentage of failures for a project. Instead, they define Acceptance Criteria—the specific size and type of defect allowed within a single weld.
Common Acceptance Criteria for RT (Radiographic Testing):
Feature ASME B31.3 (Normal Fluid Service)
Cracks None allowed (0 tolerance).
Lack of Fusion Generally not allowed.
Incomplete Penetration Limited to specific lengths (e.g., 1.5 inches in any 12-inch weld).
Slag Inclusions Limited based on pipe wall thickness (T).
Porosity Defined by specific charts comparing pore size and distribution.
The “Cost of Quality” Factor
From a management perspective, the “acceptable” rate is often driven by the budget.
Repair Cost: Repairing a weld is often 3 to 5 times more expensive than doing it right the first time due to gouging, re-prepping, re-welding, and the cost of a second RT crew.
Progressive Sampling: Many codes require “Random RT” (e.g., 5% or 10% of welds). However, if one weld fails, the code often mandates two more welds from the same welder be tested. This “penalty” system can quickly turn a 10% RT requirement into 100% RT if the rejection rate is high.
Key Factors Influencing Rates
If your rejection rate is climbing, it is usually due to one of three things:
1) Environmental Conditions: Wind or humidity affecting gas shielding.
2) Material Issues: Dirty pipe, poor beveling, or improper electrode storage (especially for low-hydrogen rods).
3) Human Element: Fatigue, tight spaces, or “mirror welding” requirements.
Note: If you are tracking a specific project, ensure you are distinguishing between the Weld Repair Rate (linear inches of repair vs. total inches welded) and the Joint Repair Rate (number of failed joints vs. total joints). The Joint Repair Rate is usually higher and more commonly cited in field reports.